The effect of current density on the structure of nickel electrolytic foams and their catalytic properties during hydrogen production

Abstract

The effect of current density on the regularities of nickel foam deposition processes has been studied. Porous nickel foams were obtained by electrochemical deposition in the galvanostatic mode at current densities of 0.3, 0.6, 0.9, and 1.2 A cm-2. The obtained deposits were characterized by high porosity and well adherence to the substrate material. The electrolytic foams had macro- and micropores. The features of the formation of the macropore system have been studied. It has been established that at low hydrogen evolution rates, a gradual formation of a porous structure occurs. While at higher rates, the formation of the matrix structure ends in the first minutes of electrolysis. It was shown that the log-normal distribution can be used to describe the formation of a hydrogen template as a system of macropores in electrolytic nickel foams over a wide range of current densities. A technique for the estimation of nickel foam macroporosity based on the data on the fraction of the surface occupied by macropores is proposed. The total porosity of deposits was calculated based on the data on the mass and volume of electrolytic foams. The catalytic activity of the obtained porous electrodes towards the hydrogen evolution reaction was analysed in an alkali solution. The value of depolarization at a current density of 0.3 A·cm–2 was used as a criterion for the efficiency of nickel foams. The value of depolarization for the obtained deposits varies in a wide range from 170 to 400 mV and strongly depends on the conditions of foam synthesis and their thickness. It has been established that nickel foams obtained at 1.2 A·cm–2 exhibit the best catalytic properties due to their uniform structure characterized by a large number of macropores evenly distributed throughout the foam volume. This ensures maximum access of the reacting particles to the electrode surface.

Keywords

• porosity
• nickel
• electrodeposition
• catalytic properties
• depolarization